Tidied up views.

* Somewhat more PEP8 compliant.
Refactored Django forms.
Extracted `cards` app urls.
Added missing template
Added basic long polling for dev.
Extracted get_game and get_player_name into a mixin
Hacky fix for new players joining games.
Merge branch 'master' of https://github.com/mralex/cards-against-django into mralex-master
Added correct stuff to form for leaving game.